This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
The subject matter disclosed herein relates to fluid handling, and, more particularly, to systems and methods for pumping used drilling fluids (“drilling mud”) from the sea floor to the surface in subsea dual gradient drilling applications.
Drilling mud is used in oil and gas drilling applications to provide hydraulic power, cooling, kick prevention, and to carry cuttings away from the cutting head. In subsea drilling applications, drilling mud is typically pumped from a rig or ship at the surface of the water down to the cutting head via a drill string. The used drilling mud and the cuttings then flow back up through an annulus between the drill string and a casing.
In riser drilling applications, the mud is pumped all the way back up to the rig or ship at the surface via the annulus. However, pumping the mud to the surface through the annulus, especially in applications having greater depths, uses large pumps and thick riser piping while causing high bottom hole hydrostatic pressure. The high internal pressures may lead to degradation and damage of the formation.
In dual gradient drilling applications, the mud is only pumped back up through the annulus to the sea floor. A diaphragm, disc pump, or centrifugal pump is then used to pump the used mud back up to the surface via a mud return line. The lifespan of a diaphragm pump may be cut short by rupturing of the diaphragm. Repair or replacement of the diaphragm pump at the sea floor may be expensive, time consuming, and a logistical challenge. Disc pumps, on the other hand, may only be 15% to 25% efficient, resulting in large disc pumps, and excess heat that heats the fluids. Accordingly, further development of pumps for dual gradient drilling applications is desired.